Study On Synthesis And Optical Property Regulation Of New High Efficiency Lead-free Double Perovskite

In recent years,the halide perovskite light-emitting materials have made great progress in basic research and device applications such as photodetectors,light-emitting diodes and lasers.The control of the luminescence properties of these materials is closely related to the selection of material components.The wavelength tuning ability covering the visible light range can be shown by anion exchange,and the excellent optoelectronic properties have attracted wide attention.However,this kind of materials pose a great threat to human health and ecological environment because of its lead-containing toxicity,and weak stability has become a great obstacle to commercial application.Therefore,the search and development of lead-free perovskite has become the focus of research.Compared with lead halide perovskite,lead-free double perovskite attracts people's attention because of its high stability and good environmental protection performance.However,these emerging semiconductors show indirect and large band gaps,which limits their applications in optoelectronics.Therefore,in this paper,the doping route is used to design the band gap to improve the photoluminescence?PL?characteristics.The details are as follows:1.The alloy Cs₂Na_1-xAg_xBiCl₆ double perovskite was formed by Na⁺doping by hydrothermal method,and the orange luminescence with the emission peak at 610 nm was obtained.by optimizing the experimental conditions,the component-dependent luminescence of Cs₂Na_1-xAg_xBiCl₆showed the maximum luminescence intensity at the feed ratio of Na/Ag=7,Due to the self-trapped exciton recombination,there is a wide emission band in the range of 500?900nm.The crystal structure,optical properties and luminescence mechanism of the alloy were studied.It is found that the lattice thermal expansion of Cs₂Na_1-xAg_xBiCl₆ exhibits an abnormal blue shift of the emission peak due to the increase of temperature,this has important physical significance for further understanding the physical properties of self-trapped excitons emission in double perovskite.2.After doping Mn²⁺ions into the alloy Cs₂Na_1-xAg_xBiCl₆,it is found that there are always two emission bands in the emission spectra,namely Mn²⁺emission and self-trapped exciton emission.By means of variable temperature fluorescence spectra,variable temperature lifetime and transient absorption spectra,we propose a kind of energy transfer of electrons from Mn²⁺ion guest to double perovskite host in double perovskite,which is different from the energy transfer from host to guest,thus the domination of Mn²⁺emission on self-trapped excitons is obtained.This work reveals a new energy transfer mechanism between the perovskite host and the doped guest.In addition,Mn²⁺:Cs₂Na_1-xAg_xBiCl₆ shows good stability in crystal structure and luminescence in open environment.3.Lead-free double perovskite Mn²⁺:Cs₂NaBiCl₆ crystals were prepared by hydrothermal method.Yellow emission with a maximum fluorescence quantum efficiency of 61%was obtained by changing the feed ratio of Mn/Bi.Its structure,composition and stability were characterized,and the luminescence temperature-dependent characteristics of Mn²⁺:Cs₂NaBiCl₆ were studied.Due to the existence of bound states between the band edge and the ⁴T₁ energy level of Mn²⁺,the abnormal emission intensity of Mn²⁺increases first and then decreases with the increase of temperature.The luminescence mechanism of Mn²⁺:Cs₂NaBiCl₆ is further analyzed.